1. Field of the Invention
The present invention relates to a bipolar electrolyzer comprising a plurality of unit electrolyzers. More particularly, the present invention relates to a bipolar electrolzyer suitable for producing chloride and alkali hydroxide by electrolyzing an aqueous solution of an alkali metal chloride, which comprises a plurality of unit electrolyzer connected with each other by an explosion-welded spring-type metal plate coupled by explosion-welding and multi-layered electric conduction plates maintaining the current density and the concentration of the electrolyte uniformly, current distribution frame protecting the cation exchange membrane and maintaining the current uniformly, and a slanted frame wall disposed within each unit electrolyzer.
2. Description of Prior Art
There have been many prior art patents related to the bipolar electrolyzer to produce chlorine and alkali metal such as caustic potash comprising an anode compartment, a cathode compartment and cation exchange membrane disposed therebetween, low-current high-voltage electric power being supplied to anode of one end unit electrolyzer and cathode of the other end unit electrolyzer and the cation exchange membrane being used as the separation membrane.
Particularly, as the prior patents regarding electrical connection between the unit electrolyzers, U.S. Pat. No. 4,111,779 discloses an electrolyzer in which the material of the partition wall of one side unit electrolyzer is titanium and the material of the partition wall of the opposite side unit electrolyzer is iron and the whole partition walls are joined together by explosion-welding.
Also, European Pat. No. 0172495 discloses a electrolyzer in which electrical connection is provided by inserting a noded plate between partition plate.
Moreover, German Pat. No. 2551234 discloses an electrolyzer in which the unit electrolyzers of plastic material are electrically connected by securing means such as bolts and nuts. Finally, Japanese Laid-Open Patent 54-90079 discloses an electrolyzer having the connecting parts made of ultrasonic welding or titanium-copper-stainless steel.
On the other hand, as prior patent regarding the inside of electrolyzer, particularly, the structure of electrical conductor is located between the electrode and electrolyte partition wall, European pat. No. 220,659 discloses an electrolyzer having the electrical conductor of a single plate in which a plurality of openings are formed. U.S. Pat. No. 4,389,289 discloses an electrolyzer having the electrical conductor of a single plate in which cavities are formed at both sides. Also, U.S. Pat. No. 4,417,960 discloses an electrolyzer having the frame type electrical conductor.
Further, as the prior patent regarding the shape of bipolar walls for a bipolar electrolyzer, an electrolyzer whose bipolar walls are manufactured by explosion-welding and the anode compartment and the cathode compartment can not be isolated is known (S. Ogawa, Chem. Age, India, 31 1980 441:K, MOTANY. ibid 31, 1980,457).
U.S. Pat. No. 4,568,434 discloses an electrolyzer of which bipolar walls are manufactured by explosion-welding and the anode compartment and the cathode compartment can be isolated. An electrolyzer whose bipolar walls are not joined by explosion-welding and the anode compartment and the cathode compartment can be isolated is also known (Journal of Electrochemistry 12, 1982,631).
Moreover, U.S. Pat. No. 4,105,515 discloses an electrolyzer which can reduce the voltage of the electrolzyer by reducing the bubble size of chlorine gas by operating the inner pressure of the electrolyzer higher than the atmosphere pressure.
An electrolyzer must have high performance, convenience in operation and the manufacturing or maintenance cost should be low. However, most of the above mentioned patents do not satisfy these above requirements. High performance electrolyzer having the partition wall of explosion-welding has the problem of high manufacturing cost due to much time and manpower of explosion-welding. An electrolyzer having the partition wall without explosion-welding has the advantage of low manufacturing and maintenance cost, but has the problem of low performance.
In case of manufacturing unit electrolyzers with plastic material, because the partition walls of the electrolyzer should be made thick considering its mechanical strength, it is impossible to manufacture a thin and small electrolyzer. Therefore, this type of electrolyzer is restricted to only a big electrolyzer. Furthermore, during the operation of an electrolyzer comprising a plurality of unit electrolyzer connected in series, if one unit electrolyzer causes any problem, the trouble shooting must be proceeded after stopping all the unit electrolyzers connected directly to it. Therefore, it causes the problem of bad working conditions.
In the conventional electrolyzer, the electrodes (1 mm thickness) and electrical conduction plates (2 mm thickness) are welded directly. However, it is very difficult to weld them together and the welded state is very poor. Further, this method not only lowers the performance of the electrolyzer, but also deteriorates the stability of whole electrolyzer system. If the inner pressure of electrolyzer is at the level of 0.5 kg/m.sup.2, the electrodes and electrical conduction plate are separated and causes the problem of local heating. Consequently, the heat damages the membrane significantly which results in stability problems for the whole electrolyzer system.